<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>div</title>
    <style>
     p{
        width:30px;
        height:30px;
        background-color: brown;
     }
     h{
        color:red;
        height:30px;
        width:30px;
     .my01{
        width:30px;
        height:30px;
        background-color:black;
     }
    </style>
</head>
<body>
    <h1 class="my01">h</h1>
    <h2 class="my01">h</h2>
    <h3 class="my01">h</h3>
    <span id="s1s">s1标签</span><br>
    <p></p><br>
    <p></p><br>
</body>
</html>